As microprocessors continue to evolve, their use in a wide variety of control applications becomes more pervasive. Various industries, such as the automotive and heavy-duty trucking industries, have continued to utilize the increasing computational speeds available at decreasing prices to afford the vehicle operator with a variety of enhanced safety features and conveniences. Manufacturers continually strive to differentiate their unique enhancements, features, and implementations from those of competitors often resulting in proprietary vehicle systems and subsystems which are difficult to integrate. The norm in the heavy-duty trucking industry is for vehicle purchasers to specify individual systems and subsystems which may be produced by different manufacturers. For example, a customer may specify one engine manufacturer, another transmission manufacturer, and a third axle manufacturer. This necessitates cooperation among the selected vehicle systems which is facilitated by the promulgation of industry standards or recommended practices.
A number of standards organizations have attempted to standardize vehicle system components and their associated methods of operation. Unfortunately, efforts of various standardization committees often lag the rapid pace of technology development and are in effect de facto standards. Thus, many systems designed according to developing standards, guidelines, or recommendations are not amenable to integration or adaptation with newly developed technology. It is therefore desirable for such new components, systems, and methods of operation to be capable of being adapted to existing vehicles without significantly affecting the price, performance, or operation of the new technology.
As standards, recommendations, and guidelines are developed, they typically undergo significant revisions and modifications. A system designed to conform with any particular draft of a standard may not be entirely compatible with subsequent revisions, additions or modifications. Furthermore, different organizations may have different opinions regarding which system, protocol, or method of operation is more desirable leading to promulgation of incompatible "standards". Thus, it is often desirable to design configurable systems which conform to various recommendations or specifications which may be published by different standards committees or as draft proposals during development.
Electronically controlled internal-combustion engines are well established in the art and have been used in various types of vehicles, including heavy-duty tractor semi-trailer vehicles, for a number of years. As such, standards, recommendations, guidelines, specifications, and the like, hereinafter collectively referred to as standards, are continually developed and published by various organizations. These standards designate component characteristics, testing procedures, and methods of operation. Such organizations include the International Standards Organization (ISO), the Society of Automotive Engineers (SAE), and the Institute for Electrical and Electronics Engineers (IEEE), among numerous others. Often standards published by one organization will have corresponding designations in other organizations or may be a conglomeration of various other standards. Standards of particular interest in providing electronic engine control for vehicles such as heavy-duty tractor semi-trailer vehicles are published by the SAE and designated SAE J1922 and SAE J1939. The J1922 standard is an interim standard, eventually to be supplanted by the J1939 standard when finalized. As such, the J1922 and J1939 standards include a number of similarities in prescribing control system design and operation for compression-ignition internal-combustion engines, such as diesel engines. As is known, ISO 11898 is generally similar to and compatible with SAE J1939.
The J1922 and J1939 standards define various control modes for electronically controlled engines including a normal mode, a speed control mode, a torque control mode, and a speed and torque limit control mode. In normal mode, engine fueling is controlled based primarily on input received from the vehicle operator, typically via an accelerator pedal. Of course a number of other factors influence the actual determination of engine fueling as described in greater detail below. In speed control mode, engine fueling is controlled to maintain a substantially constant engine speed. In torque control mode, a substantially constant engine output torque (as a percentage of total available torque) is effected regardless of engine speed and vehicle speed. Speed and torque limit control mode imposes an upper limit on engine speed and/or engine output torque. The override modes may be used to override the current operating mode and command the engine to a particular engine speed or engine output torque. The control mode is based on current operating conditions and commands received by the engine controller which may be generated by various other vehicle systems and subsystems or by the vehicle operator. A more detailed description of the modes of operation may be found in the J1922 and J1939 specifications published by the SAE, the disclosures of which are hereby incorporated by reference in their entirety. Other, related standards utilized in electronic engine control and communication include SAE J1587, SAE J1708, and SAE J1843, the disclosures of which are also hereby incorporated by reference in their entirety.
Traditional cruise control functions are implemented by the engine controller and utilized to automatically maintain a desired road speed or a desired engine speed without the need for operator intervention. Typically, an on/off switch is provided for the cruise control in addition to a switch which sets the desired vehicle speed or engine speed to the current operating speed when the switch is actuated. Some systems provide an additional switch for incremental speed adjustments and automatically returning to a previously set speed.
Under steady driving conditions, the use of cruise control may reduce driver fatigue and improve comfort while also enhancing fuel economy in many applications. However, an ever-increasing traffic volume often results in congested roadways which reduces or eliminates opportunities for maintaining a preset fixed speed over a long period of time, thereby limiting the associated advantages of cruise control. Furthermore, vehicle operators are likely to avoid using cruise control in marginal conditions when traffic continually slows and accelerates due to the need for repeated driver intervention to set and reset the cruise control, even if these events are separated by several minutes. Thus, providing a cruise control system and method which could accommodate variations in traffic speed would allow increased cruise control utilization and a corresponding increase of attendant benefits.
Recent advancements in cruise control technology have resulted in systems which are capable of measuring and maintaining a substantially constant following distance or headway distance relative to a forward vehicle. Headway distance is determined based on the current vehicle speed and closure rate and is often designated in seconds while following distance is independent of speed and closure rate and is designated in feet. These so-called intelligent or adaptive cruise control functions typically utilize an electromagnetic beam, such as a laser beam, a microwave radar beam, or a video image, to determine the inter-vehicle distance and closure rate between the host vehicle and one or more forward vehicles. This information may be used to automatically adapt to the traffic flow and "track" or follow the forward vehicle at a desired following distance selected by the operator. Distance and closure rate information may also be used to warn the vehicle operator of a potentially hazardous situation such as following the forward vehicle too closely for the current vehicle speed or approaching the forward vehicle or another object too rapidly such that a collision may occur.
Some prior art intelligent cruise control systems are designed for custom applications which require complete system integration when th e vehicle is de signed, manufactured, and assembled. In these systems, the intelligent cruise control module may control vehicle acceleration/deceleration through a customized engine control module which may implement an intelligent cruise control algorithm to modify engine fueling or effect vehicle braking. These systems, however, fail to provide a system which may be installed without significant changes to currently available engine control modules. furthermore, these systems are difficult to retrofit or may be completely incompatible with existing vehicles without significant system modification and expense, particularly in medium and heavy-duty truck applications employing diesel engines. Thus, it is desirable to have a system and method for implementing an intelligent cruise control function in vehicles which may or may not have traditional cruise control functions, without substantial system modification.